煤层气井水力压裂有效消突边界物理模型

针对低渗煤储层煤层气井水力压裂裂缝扩展范围和消突边界确定问题,以潞安矿区煤层气井为例,采用微地震裂缝实时监测数据、有限元地应力模拟技术及井下瓦斯抽采参数,对煤层气井水力压裂范围、裂缝几何形态、压裂前后地应力分布进行研究,建立了压裂裂缝扩展和消突边界物理模型,划分了菱形井网消突范围。结果表明:研究区裂缝类型属于PKN型,压裂区呈近似椭圆形,主裂缝沿最大水平主应力方向延伸,区内划分出铺砂区、最终解吸区、裂缝区、渗透区、气涌区等5边界;压裂区四周应力沿σ_H,σ_h分别升高19%和7%,区内下降15.5%和9.5%,地应力模拟结果与压裂边界物理模型相吻合;在排采达标情况下,有效消突边界小于压裂边界,与支撑剂铺置边界一致,有效消突边界之外存在突出危险区,菱形井网采用200 m×125 m布置方式更有利于井下对应区瓦斯防治。

A physical model of outburst elimination boundary after hydraulic fracturing in coal-bed methane well

In order to forecast hydraulic fracturing range and define effective outburst elimination boundary,the methods of ground stress simulation technology,micro seismic real-time monitoring data and gas drainage parameters analysis were applied to build the physical models of fracture extending & hydraulic fracturing boundary and to determine different dangerous regions on rhombus well pattern by analyzing the control range of hydraulic fracturing,fracture morphology and stress distribution before and after hydraulic fracturing in single coal-bed methane wells with low permeability coal reservoir at Luan mining area.The results showed that the fracturing area of single hydraulic well was similar to an elliptical shape;the main fracture extended along the direction of the maximum horizontal principal stress;the fracturing area was divided into five boundaries including laying sand zone,final desorption zone,fracture zone,penetration zone and gas surge zone;the stress value around fracturing zone along σH and σh raised about 19% and 7%,and stress value in fracturing zone declined about 15.5% and 9.5%;the boundary physical model of hydraulic fracturing was consistent with the results of ground stress simulation.In a standard gas drainage operation,the boundary of effective outburst elimination which was smaller than fracturing boundary was consistent with the laying boundary of proppant.Outside of effective outburst elimination boundary may exist outburst dangerous area,but inside of the boundary,rhombus well pattern by 200 m by 125 m arrangement is better for the mine gas prevention and control of the corresponding area.